This is an open-label, uncontrolled phase 4 study to assess the safety and immunogenicity of the Japanese encephalitis (JE) vaccine Ixiaro® (IC51) in an elderly population.

Inclusion Criteria:

• Male or female subjects ≥ 65 years of age at the time of 1st vaccination of good general health status including subjects with pharmacologically controlled conditions like hypercholesterolemia, hypertension, cardiovascular disease or non insulin-dependent diabetes mellitus
• Weight: ≥ 45.5 kg and ≤ 150 kg at Visit 0 (Screening Visit)
• White blood cells ≥2,500/mm3 and <11,000/mm3 at Visit 0
• Absolute neutrophil count within normal limits at Visit 0
• Platelets within normal limits at Visit 0
• Written informed consent obtained from the subject prior to any study related procedures

Exclusion Criteria:

• History of clinical manifestation of any flavivirus infection (Yellow Fever, Dengue Fever, JE, Tick Borne Encephalitis (TBE) and West Nile Fever/Neuroinvasive Disease)
• Vaccination against JE (including study participation in any previous or current IC51/IXIARO® clinical study), Yellow fever, Dengue Fever or West Nile Fever at any time prior or during the study
• Vaccination against TBE within 30 days prior to first IXIARO® vaccination at Visit 1 (Day 0) and until Visit 3 (Day 70)
• Use of any other investigational or non-registered medicinal product within 30 days prior to IXIARO® vaccination at Visit 1 (Day 0) and throughout the entire study period
• Immunodeficiency including status post-organ-transplantation or immuno-suppressive therapy, and a family history of congenital or hereditary immunodeficiency
• Infection with the human immunodeficiency virus (HIV, a negative test result within 30 days before screening is acceptable), Hepatitis B virus (HBV, Hepatitis B surface antigen [HBsAg]) or Hepatitis C virus (HCV)
• Administration of chronic (defined as longer than 14 days) immunosuppressants or other immune-modifying drugs within 30 days prior to IXIARO® vaccination at Visit 1 (Day 0) and during the study until Visit 3 (Day 70). (For corticosteroids this means prednisone or equivalent >= 0.05 mg/kg/day; topical and inhaled steroids are allowed).
• Periodic steroid injections, e.g., intra-articular, are not allowed within 30 days prior to first IXIARO® vaccination at Visit 1 (Day 0) and until Visit 3 (Day 70)
• History of autoimmune disease, including Type I Diabetes mellitus. Subjects with vitiligo or thyroid disease taking thyroid hormone replacement are not excluded.
• Acute febrile infections or exacerbation of chronic infection on the day of IXIARO® vaccination (Day 0 and Day 28)
• Skin cancer in the past six months. If treatment for skin cancer was successfully completed more than six months ago and the malignancy is considered to be cured, the subject may be enrolled. Subjects with history of skin cancer must not be vaccinated at the previous site of the malignancy.
• Any other malignancy in the past 5 years. If treatment for cancer was successfully completed more than 5 years ago and the malignancy is considered to be cured, the subject may be enrolled.
• Clinically significant hematological, renal, hepatic, pulmonary, central nervous, cardiovascular or gastrointestinal disorders, which are not adequately controlled by medical treatment within the last 12 weeks before IXIARO® vaccination at Visit 1 (Day 0) as judged by the site's Principal Investigator
• Clinically significant mental disorder not adequately controlled by medical treatment
• History of Guillain-Barré-Syndrome (GBS).
• History of severe hypersensitivity reactions, in particular to a component of the IXIARO® vaccine (e.g. protamine sulfate), anaphylaxis or severe cases of atopy requiring emergency treatment or hospital admission
• History of urticaria after hymenoptera envenomation, drugs, physical or other provocations, or of idiopathic cause
• Drug addiction within 6 months prior to Visit 0 and throughout the entire study period (including alcohol dependence, i.e. more than approximately 60 g alcohol per day, or conditions which might interfere with the study conduct)
• Inability or unwillingness to avoid more than the usual intake of alcohol (> 60 g alcohol/day) during the 48 hours after each vaccination
• Any condition which might interfere with study objectives or would limit the subject's ability to complete the study in the opinion of the investigator
• Persons who are committed to an institution (by virtue of an order issued either by the judicial or the administrative authorities) will not participate in the study